水すい面めん下か

noun, noun which may take the genitive case particle 'no'

underwater; below the water surface

Literal physical location beneath the surface of water.

• 水すい面めん下かの岩いわに注ちゅう意いしてください。

  Watch out for rocks below the water surface.

noun, noun which may take the genitive case particle 'no'

behind the scenes; behind closed doors; below the surface

Figurative use for activities or negotiations that are not publicly visible; often implies hidden maneuvering or preliminary work.